A left visual field bias for semantic encoding of unattended words

Previous studies have shown that verbal processing in both normal individuals and a split-brain patient can be strongly affected by the semantic category of an unattended word presented to the left visual field (LVF). The effect was interpreted in terms of inhibition, since responses were slower when the unattended LVF word belonged to the same category as the target word. The present experiment discriminated between two alternative explanations for this finding. Subjects were presented with two letter strings, one in central vision and one to the left or right of centre. Subjects made a speeded lexical decision to the central string, and were instructed to ignore the lateral string. When a word was presented to the LVF subjects responded more slowly when it was semantically related to the central word. When an unattended word was presented to the RVF, its semantic relationship to the central word had no effect on decision latency. This finding is discussed in relation to views of performance laterality and selective attention.